Not applicable.
This invention relates to piles generally and, in particular, to a method of and apparatus for the real-time analysis of driven piles.
Piles are commonly used to support a wide variety of load bearing structures, such as bridges. Accordingly, piles must be driven to sufficient depths to provide a desired load bearing capacity, without substantially damaging the pile during the driving process. It is customary to characterize pile parameters such as accelerations, strains, pile capacity, stresses within the pile, energy applied to the pile and the average displacement per blow (xe2x80x9cblow countxe2x80x9d) of a driven test pile to determine pile driving process parameters. Pile driving process parameters include the force applied by the driving hammer to the pile and the number of blows required. The force applied by the driving hammer to the pile is referred to as the stroke (or hammer stroke) for a hydraulic hammer and the fuel setting for a diesel hammer. The determined pile driving process parameters are then applied to a plurality of piles during the driving process.
Pile parameters are conventionally measured by mounting sensors on the top of a test pile. The sensors produce raw pile data. Sensor data is supplied to a pile driver analyzer through a hard-wired connection and is used to determine pile parameters which are derived from the supplied raw pile data. Pile driving analyzers can each cost approximately $40,000 to $100,000.
Accelerometers are sensors which are generally used to measure pile acceleration, which can be converted (through integration twice) into the displacement of piles being driven (e.g. into the earth) by a pile driving hammer. An accelerometer is typically mounted near the top of a test pile, the accelerometer wired to an analyzer, such as a pile driver analyzer. From raw pile data, the pile driving analyzer can determine the efficiency of the pile driving hammer, accelerations, driving resistance of the pile (capacity), stresses in the pile as well as other useful pile parameters. In the case of capacity, soil resistance results from both the sides and the tip (bottom) of the pile, the soil resistance being a function of pile depth.
Conventional systems for measuring driving resistance and pile velocity (which can be integrated to produce displacement) utilize self-generating-type accelerometers, which, as the name implies, self-generate direct current electric signals. A quartz or piezoelectric crystal is compressed by the forces generated by the mass of the accelerometer during movements of the pile, producing electrical impulses which are proportional to the acceleration of the pile. The acceleration signals produced by the accelerometer mounted on a test pile are recorded and subsequently electronically integrated through a wired connection to separate equipment (e.g. pile driver analyzer) to produce a velocity measurement. The velocity measurements are in turn, electronically integrated a second time to produce a measurement of pile displacement. The number of recorded blows are determined for each linear unit of displacement to arrive at the blow count.
The force applied to the pile by the pile driving hammer is generally sensed simultaneously by separate apparatus, such as a strain gauge. A strain gauge may be mounted near the top of a test pile disposed orthogonal to the accelerometers. The strain gauge is wired to an analyzer, such as a pile driver analyzer, and used to determine strains, stresses and forces. The force and average displacement can be converted by an analyzer into a driving resistance by known formulas which recognize soil conditions, pile configuration and desired depth of penetration.
As a pile is driven into a material (e.g. earth), the force of the blows applied must also be controlled to avoid exceeding the elastic limit of the pile material. Otherwise, costly damage to the pile can occur, such as to the pile tip or to any portion of the pile length due, for example, to the vibrational energy transmitted by the back reflected wave. To help minimize such damage, drive caps are fitted over the head of the pile to more evenly transmit the hammer blows to the pile and to cushion the blows, while at the same time maintaining the head of the pile in alignment with the hammer by guiding the head parallel to the leads frame and retaining the pile in a substantially straight predetermined path.
Although the use of caps (e.g. steel caps) with cushions and maintaining proper alignment of the hammer and the pile with the aid of leads helps to mitigate pile damage, the burden in most cases falls largely upon the experience of the operator to determine the driving force required. For a given set of conditions, one or more test piles may be used to help guide the operator. Strain gauges mounted on sample piles are commonly used to determine the force of blows and the dynamic forces within piles.
However, strain gauges can fail to register the presence of transmitted waves. For example, two waves can destructively interfere at any point along a pile so that no net stress results when a forward wave is met by a back reflected wave having an equivalent magnitude. Specifically, a compressional wave pointing down the pile can be offset in whole or in part by a tension wave pointing up the pile. In the case of two or more waves which offset, a device capable of measuring pile displacement, such as an accelerometer, can be used to identify the stressless dynamic condition.
Strain gauges must generally be screwed or otherwise attached to the pile and wired to a pile driving analyzer. Thus, the process of properly mounting strain gauges is a relatively time consuming and costly process. The strain gauge is also generally a very fragile device and its reliability under the repetitive dynamic shock loading to which the pile is subjected can be easily compromised.
Even after a pile is driven to a desired depth based on data derived from a test pile, it is generally desirable to measure the actual static bearing load which the driven pile can support mainly because of variability in the ground condition. This is usually done by loading a test pile with increasing weight until it moves. This is called a dead load bearing test, which is a time-consuming and expensive process.
As noted earlier, piles driven subsequent to the test pile are generally driven without measuring pile parameters during the driving process. Due to variation in parameters such as the ground condition between areas within a given construction area, piles tend to be driven less or more than the test pile under the same pile driving process parameters (e.g. number of blows and stroke). This can result in undesired results such as loss in capacity and unnecessary expense or pile damage, respectively. In addition, since sensors are also not generally provided to piles which are placed in field service, pile integrity cannot be measured during the service lifetime of piles. Accordingly, damaged piles, which can potentially lead to the collapse of a structure supported by the damaged pile, are typically not detectable while the pile is in service.
A system for the determination of pile parameters includes at least one structure for measuring pile data, the structure for measuring pile data disposed within measurement range from at least one pile. A wireless transmitter is adapted to transmit the pile data, the wireless transmitter communicably connected to the structure for measuring pile data. At least one remotely located wireless receiver is provided for receiving the transmitted pile data.
The system can include a device for determining at least one pile parameter from the pile data, the device being communicably connected to the remotely located wireless receiver. The structure for measuring pile data can include at least one strain gauge. Transmissions from the wireless transmitter can include information which can be identified with the location of specific piles.
The transmitter can be a broadband transmitter, and the system can include a multiplexer for combining pile data from a plurality of structures for measuring pile data into one signal for transmission. Structures for measuring pile data can be positioned substantially within piles.
The system can further include a wireless receiver adapted to receive triggering signals, receipt of the triggering signals directing the structure for measuring pile data to commence measurement of pile data. Structures for measuring pile data can be adjacent to a bottom portion of the pile and/or positioned adjacent to a top portion of the pile. At least one structure for measuring pile data can be disposed between the structure for measuring pile data adjacent to a bottom portion of the pile and the structure for measuring pile data adjacent to a top portion of the pile. When at least one structure for measuring pile data is positioned adjacent to a bottom portion of the pile, the structure for measuring pile data adjacent to a bottom portion of the pile can be positioned below the ground level. In a preferred embodiment of the invention, pile data can be digitally encoded prior to transmission by the wireless transmitter.
An apparatus for supporting load bearing structures includes at least one pile and at least one structure for measuring data from the pile. The structure for measuring pile data as disposed within measurement range from the pile. A wireless transmitter is communicably connected to the structure for measuring pile data. At least one remotely located wireless receiver is provided for receiving the transmitted pile data. The system can further include a device for determining at least one pile parameter from the pile data, the device communicably connected to the remotely located wireless receiver. The structure for measuring pile data can include at least one strain gauge. Transmissions from the wireless transmitter include information which can be identified with the location of specific piles.
The wireless transmitter can be a broadband transmitter and the apparatus can further include a multiplexer for combining pile data from a plurality of the structures for measuring pile data into one signal for transmission. In a preferred embodiment of the invention, pile data is digitally encoded prior to transmission by the wireless transmitter.
At least one of the structures for measuring pile data can be positioned substantially within the pile. The pile can have at least one open volume within the pile, the open volume adapted for receipt of the structure for measuring pile data. The volume with the pile can include at least one longitudinally oriented volume. The apparatus can further include a wireless receiver adapted to receive triggering signals, the receipt of triggering signals directing the structure for measuring pile data to commence measurement of pile data.
At least one structure for measuring pile data can be positioned adjacent to a bottom portion of the pile and/or at least one structure for measuring pile data can be positioned adjacent to a top portion of the pile. When structures for measuring pile data are positioned on both top and bottom positions of a pile, at least one structure for measuring pile data can be disposed between the structures for measuring pile data. At least one structure for measuring pile data can be positioned adjacent to a bottom portion of the pile, the structure for measuring pile data being below the ground level.
An apparatus for supporting load bearing structures includes at least one pile and at least one structure for measuring pile data. At least one of the structures for measuring pile data is mounted to or substantially within the pile. A transmitter is provided which is communicably connected to the structure for measuring pile data. The transmitter can be wireless transmitter, the wireless transmitter for transmitting pile data to at least one remotely located receiver. The transmitter can be a broadband transmitter, and the apparatus can also include a multiplexer for combining pile data from a plurality of structures for measuring pile data into one signal for transmission. In a preferred embodiment of the invention, pile data can be digitally encoded prior to transmission by the transmitter. The receiver can be communicably connected to a device for determining at least one pile parameter from the pile data.
A system for the measurement of pile parameters, includes a pile and at least one structure for measuring pile data. At least one of structure for measuring pile data is mounted substantially to or within the pile. A transmitter is communicably connected to the structure for measuring pile data for transmitting pile data to at least one remotely located receiver. The remotely located receiver is communicably connected to a device for determining at least one pile parameter from the pile data. The transmitter can be a wireless transmitter.
The transmitter can be a broadband transmitter and the apparatus also include a multiplexer for combining pile data from a plurality of structures for measuring pile data into one signal for transmission. In a preferred embodiment of the invention, pile data can be digitally encoded prior to transmission by the transmitter.
At least one structure for measuring pile data can be disposed substantially at the bottom end of the pile. The structure for measuring pile data disposed at the bottom of the pile can be mounted substantially within the pile.
A method of forming piles with sensors mounted substantially within includes the steps of providing at least one sensor for measuring pile data, positioning the sensor in a location which will be substantially surrounded by pile material after application of the pile material, and substantially surrounding the sensor with the pile material. The sensor can be positioned at an interior location in a pile frame in the positioning step.
The surrounding step can include a casting step. The providing step can include providing a transmitter, the transmitter communicably connected to the sensor. The transmitter can be a broadband transmitter, and the providing step can further include a multiplexer for combining pile data from a plurality of the structures for measuring pile data into one signal for transmission.
A method for the wireless determination of pile parameters includes the steps of providing at least one structure for measuring pile data, the structure for measuring pile data within measurement range from a pile, and a wireless transmitter communicably connected to the structure for measuring pile data, and wireless transmitting the pile data to at least one remote receiver by the wireless transmitter. The method can further include the steps of providing the received pile data from the remote receiver to a computing device, and determining at least one pile parameter by the computing device. Preferably, the transmitting, the directing and the determining steps are automatic. The determining step can further include using the pile parameters determined in the determining step to determine at least one pile driving process parameter for use during pile driving. The pile driving process parameter can include a force applied by a driving hammer to a pile.
The pile can support a structure, wherein the transmitting, the directing and the determining steps are performed after installation of a pile. The transmitting, directing and the determining steps can be performed real-time and can be performed responsive to a received excitation signal. The received excitation signal can have a threshold. Above a predetermined threshold excitation to the transmitting, directing and determining steps are initiated. The received excitation can include information which can be identified for selective processing by specific piles. Transmissions during the transmitting step can include information for determining the location of specific piles and the method can further include the step of determining the location of specific piles from received pile data transmissions. The method can further include the step of using at least one of the determined pile parameters to determine at least one pile driving parameter.
A method for driving piles includes the steps of providing at least one structure for measuring pile data, the structure for measuring pile data within measurement range from a pile and a wireless transmitter communicably connected to the structure for measuring pile data. Pile data is wirelessly transmitted to at least one remote receiver by the wireless transmitter and at least one pile driving process parameter is determined from the pile data. The pile is driven using the pile driving process parameters. The wirelessly transmitting and the determining steps can be performed automatically. The driving step can be automatic. The pile driving process parameters can include a force applied by a driving hammer to the pile. The method can include the step of adjusting the force applied between blows of a driving hammer. The step of adjusting the force applied can be based at least in part on determined pile parameters.